A. Field of the Invention
This invention relates to a method and apparatus for recovering waste oil, and more particularly to a method and apparatus for recovering oil from a mixture of oil, water, including emulsions of oil and water, and suspended solids and polymers.
B. Description of the Prior Art
During operations at refineries and petro chemical plants, spills of oil and various petroleum products are inevitable. The spilled oil and products becomes mixed with water from rainfall and other sources and eventually flow into sewers at the refinery or plant. The mixture of oil, products, and water typically includes sand, silt, rust, dust, catalyst fines and other solids. Additionally, some of the products are relatively low density polymers, which become mixed with the oil, water, and solids. The mixture also contains various emulsions of oil and water.
Because of environmental considerations and governmental regulations, the contents of the sewers at the refineries and plants may not be discharged to municipal sewer systems or to nature drainage. Rather, the sewer contents must be collected for disposal or processing by the refinery or plant operator. The refineries or plants normally have devices called interceptors that are used to separator water from oil. However, the emulsions of oil and water are difficult to break and cannot be separated in the interceptor. Also, even after processing through the interceptor, both the water and the oil are heavily contaminated with particulate matter and polymers. Accordingly, after processing in the interceptor, neither the water nor the oil are suitable for reuse or nonpolluting discharge to natural drainage.
Attempts have been made to achieve better separation of the oil and water; however, these attempts have been less than satisfactory. The attempts involve heating the mixture, adding various chemicals to the mixture, and allowing the heated chemically treated mixture to stand for a time such that the material separates by gravity into layers of oil, water, and sludge. However, the foregoing attempts have been only partially successful in breaking the emulsions. Only a relatively small portion of the emulsions are separated into oil and water. The reason for this difficulty lies apparently in the fact that the emulsions are held together by suspended particulate matter which is wetted by or has an affinity for both oil and water. Known treatment methods are ineffective in breaking such emulsions. Moreover, neither the oil nor the water after such treatment are suitable for reuse.
Accordingly, it is an object of the present invention to provide a method and apparatus for treating refinery and petrochemical wastes that overcome the shortcomings of the prior art. It is a further object of the present invention to provide a method and apparatus for treating mixtures of oil, water, and dissolved and suspended solids to yield substantially clean oil and water. It is yet a further object of the present invention to provide a method and apparatus that will break emulsions that are held together by suspended particulate matter.